This invention relates to a fan blade for an aircraft engine.
Aircraft engines must be able to withstand a fan blade loss. A fan blade loss occurs when a blade of a fan breaks and blade segments separate, which can lead to considerable damage to the engine and to the entire aircraft. In the event of a fan blade loss of all-metal fan blades in particular, the mass of the lost fan blade, which lies proportionately far to the outside radially, causes high impact forces into the fan casing. To compensate for that, a relatively heavy fan casing, a strong front mounting structure and a relatively heavy fan rotor are required. These cause high imbalance forces introduced into the engine suspension on the aircraft side, which in turn leads to the requirement to design the engine suspension relatively heavy and solid.
The weight and costs of the engine and the engine suspension are therefore considerably increased by the necessity to compensate for a fan blade loss.
Accordingly, there is a need to reduce the disadvantages entailed by compensating for a fan blade loss.
To do so, it is known to design fan blades not in solid metal, but in a hybrid manner, thereby reducing their weight. For example, US 2014/0072427 A1 describes the provision of a honeycomb filler inside recesses of all-metal fan blades. U.S. Pat. No. 5,913,661 A describes grooves made in a fan blade and filled with an elastomer, which serve to damp fan blade vibrations. Further hybrid structures of fan blades are described by U.S. Pat. No. 8,500,410 B2, U.S. Pat. No. 6,364,616 B1 and U.S. Pat. No. 5,655,883 A.
The solutions known in the state of the art for providing hybrid fan blades however involve some disadvantages. For example, honeycomb fillers, which according to US 2014/0072427 A1 are incorporated in suction-side recesses of fan blades, are unsuitable for damping against blade vibrations and prone to cracking when overstretched, e.g. in the event of a bird strike. Grooves made in the main body of the fan blade according to U.S. Pat. No. 5,913,661 A also harbour the risk of cracking in the event of being overstretched, e.g. from a bird strike.